Hydraulic safety elevator



June 23, 1959 L. F. JASEPH 2,891,635

HYDRAULIC SAFETY ELEVATOR Filed Feb. 26, 1 5:

[A LII INVENTOR.

BY w yw 'ilnited Steps 2,891,635 HYDRAULIC SAFETY ELEVATOR Lawrence F. Jaseph, Memphis, Tenn., assignortdDover Corporation, Memphis, Tenn, a corporation of Delaware Application February 26; 1957',S erial No. 642,436 5 Claims. (Cl. 187-17) The present invention relates to hydraulic elevators and more particularly to the'type in which a cab is supported on a vertically movable plunger that extends upwardiy from a vertical support cylinder. Such elevators are sustained by fluid under pressure within the supporting cylinders, which usually extend down into the earth where extensive corrosion can occur withoutdetection. A cor; roded cylinder can rupture with a sudden loss of elevator supporting fluid. This possibility creates the hazard of an elevator descending at an uncontrolled rapid rate.

One object of the invention is to provide an improved elevator of the above character having a remarkably simple, economical construction which affords dependable protection against a hazardous loss of hydraulic support due to corrosive failure of the hydraulic support cylinder.

Other objects will be apparent from the following dcscription as'related to the single figure of the drawing; which shows apartially sectioned side view of the ex emplary cmbodimentof the invention.

As shown, the improved elevator comprises a cab or car positioned bet'weenvertic'al guides 12 running up" wardly from a pit 14 underlying the cab. The cab 10 is supported by its lower frame or platform structure '15 which is attached to the upper end of a cylindrical support plunger 16. The-plunger 16 extends down into" a vertical support cylinder 20. From an upper end-located in the"pit--14, the cylinder '20 passes through the-'concrete floor 22 of the pit and extends into the earth below.

The length of the cylinder 20 is adequate'to accormno date the plunger 16 when the cab 10 is in-its lowermost position. The plunger 16 itself has a 'lerigth sufiicient to provide the desired range of vertical cab movement; As shown, the inside diameter of the cylinder 20 is' substantially larger than the outside diameter of the plunger '16, thus providing annular space 24 around the plunger which is adequate for a free flow of operatingfluidbetween the upper and lower ends of the cylinder.

The annular space -24"is-closed at" the upperen'd of the cylinder 20 by anannular'plunge'r guide 26 closely encircling the" plunger 16 and bolted'to aradial'flange 28 on the cylinder. A centralcount'erbore 30 in the upper face of theguide 26 provides circumferential clearance around the plunger 16 for the inner lip of an annular seal 32 slidably engaging the plunger; Asfsho wn, the outer periphery of the seal 32 is clamped to the upper face of the'casting-26by an-annular retainer 34.'

A high pressure conduit '36 for operating fluidis connected into the upper end of the cylinder 20 just below the annular guide 26. The opposite end of the conduit 36 is connected to conventional'pumping 'andhydraulic control structure (not shown).

The-lower'endof the cylinder 20 is closed by an impervious'--outer' head 40- cut' from steel" plate. Circular in shape,-the head 40 is inserted Within the-extremelower end of .the cylinder 20 'and securely fixed to the cylinder by a circumferentially continuous fusion 'weld'42 between the cylinder and the entire. periphery of the head.

Normally the loaded plunger 16 is supported by hy- 2,891,635 Patented June 23, 1959 2. draulic fluid under pressure within the-cylinder 20. The elevator is raised by forcing additional fluid under pressure into the cylinder20 through the conduit 36. Lower ing of the elevatoris effected by exhausting'fluid' through the conduit 36.

As originally designed and installedJhe cylinder structure, including the outer head 40 on the lower end of the cylinder, has suflicient strength capacity to contain the operating fluid pressure within the cylinder with a large factor of safety appropriate to elevatordesign practice; However, initial strength capacity alone cannot assure safe operation over along servicelife, n

The cylinder 20 extends down into the earth where it cannot bein spected. There the cylinder structure in: cluding the head '40 andthe we ld 42 is subject to corrosive attack which as a practical matter cannot be precluded withabsolute certaintyby protectivevcoatings. In some instancescorrosionfrnay occur at a break-through in the protective coating used. Wet soil conditions are conducive to corrosion; Moreover, corrosion can be greatly accelerated by 'leaka'ge of direct current from the metal cylinder structure intoth e surroundingearth. If this occurs thecylinder' structure can serve as an anode, which is seriously and sometimes rapidly weakened bycorrosion.

While such corrosion may attack and weaken any portion of the cylinder structure extending into the earth, it does not necessarily produce a: hazardous condition Thus, if the continuouscylindrical wall portion of the cylinder 20'is attacked by corrosion even to the extent that theinternal fluid pressurebr'eaks through th'efcorf roded area, the breaks which: occur are ordinarily of such small size that'Qfiui'd does' not escape at a'rate suflicient to allow a hazardous descent of the elevator. I 7,

Yet a hazardous condition can arise through corrosive weakening of the extreme'lower end of the cylinder structure, particularly the peripheral weld 42' which sustains the fluid force on the outer head 40. Thus, corrosive weakening of the outer head Weld 42 "can result ina'sudden rupture or ripping :of'the entire weld without pref viouswarning. The effect of this can be a" sudden rush of fluid from the lower' end of the cylinder 20, accompanied by an'uncontrolled' haz'ardousde's'cent of the elevator." m I c I I Protection against this possible 'disastr'o'tis"eventuality is provided in the .improved elevator in an extremely eifective, yet economicalmariner.

For this purpose a circular safety head 44 is placed transversely in the lower end of the cylinder 20 a short distance above theouter'head tij The safety 'head 44 is secured to the cylinder'by a'circuinferentially continuous fusion weld" 46 between the cylinder and the en tire periphery of the safety head. Thus located within the cylinder 20, inside the outer head 40, the peripheral weld 46 is isolated from-the surrounding earth and fully pro- .tected against corrosion. I

The short vertical spacing between the protected safety head 44 and the outer head 40 provides a thin'plenuin or safety chamber 48, just above the exposed outer head. This safety chamber is'continuously maintained at the same pressure existing in the cylinder 20 above the safety head '44.

Continuous equalization of the pressure on opposite sides of the safety head44 is effected through a safety discharge orifice 50 for-med in the safety head 'and hav ing, as .willpresently appear, a predetermined size or effective flow area which provides for an unmistakable yet'safeidescentzof the elevator" in'the event of a rail-vie of the outer head 40.

As' longras tliecylinder structure includingfthe outer "head 40 remains intactythebuterhead is subject-to the full internalprcssure of'the cylinder" to the same extent as if the safety head 44 were not present. The etfect of this is to continuously test the strength of the outer head and its peripheral weld 42 by subjecting it to the full pressure existing within the cylinder. Outer head and weld structure capable of meeting this continuing test will protect the inner safety head 44 against corrosion.

While the presence of the safety head 44 does not protect the outer head 40 or its weld 42 against corrosive weakening or failure, it does provide in the event of such failure dependable protection against descent of the elevator at a hazardous rate. Thus the strength of the safety head ,4 and its peripheral weld 46 is adequate to contain the full operating pressure within the cylinder even after failure of the outer head structure.

Failure of the outer head 40 naturally releases the fluid from within the safety chamber 43. Fluid from above the safety head 44 then escapes through the safety aperture St at a rate which allows the elevator to descend at a limited speed which is not hazardous, yet adequate to provide unmistakable notice to attendant personnel that the equipment is out of order. Lowering of the elevator continues until the platform 15 engages pit bumpers 51 or until downward movement of the elevator is otherwise terminated as by engagement of the plunger 16 with the safety head. It will of course be necessary to repair the cylinder structure before the elevator can again be operated.

The safety fluid escape orifice 50 is properly dimensioned to lower the elevator safely when a differential pressure equal to that required to sustain the elevator under its full rated load will discharge fluid through the orifice at a rate which allows the plunger 16 to descend at a speed of five feet per minute. The exact size or effective flow area of the orifice which will provide for descent of the elevator at this speed is determined by a number of factors, which include the length of the orifice, the diameter of the plunger 16, the density of the hydraulic fluid used, and the fluid pressure required within the cylinder to sustain the rated load on the elevator.

To minimize the possibility of the orifice 50 becoming clogged with foreign matter and at the same time simplify its flow characteristics, it is enlarged at its down stream or lower end which communicates directly with the safety chamber 48. For a circular orifice thus formed the diameter of the orifice can be determined by the following formula:

In this formula appropriate English units are used. The symbol d is the diameter of the orifice; D is the diameter of the plunger 16; V is the safety descent speed, which should be approximately 5 ft. per minute for a fully loaded elevator; w is the mass density of the hydraulic fluid used; and p is the fluid pressure required in the cylinder to sustain the plunger 16 against descent when the elevator is loaded at its rated weight capacity.

The differential fluid pressure which arises across the safety head 44 immediately in the event of a failure of the outer head structure on the lower end of the cylinder can be used for automatically triggering other safety devices designed to preclude continued operation of the elevator. Thus as shown in the drawing, a small pres sure sensing conduit 52 is extended downwardly to the lower end of the cylinder 20 and connected through the cylinder wall to communicate with the safety or plenum chamber 48. The upper end of the conduit 52 is connected to a signal or control device 54.

As shown, this device is a differential pressure switch connected between conduit 52 from the plenum chamber 48 and the conduit 36 communicating with the upper end of the cylinder. The switch 54 is designed to operate in response to a differential pressure between the upper end of the cylinder 20 and the plenum chamber 48 which would indicate a leak or rupture in the cylinder structure below the safety head 44. Electrical leads 56 extending from the automatic switch 54 can be used in operating warning signals or elevator disabling controls of any desired character which can be readily devised by those skilled in the art. Other safety controls and indicators may be provided as desired to respond to the instant pressure within the plenum chamber 48.

While I have shown a preferred embodiment of my invention, it will be apparent that numerous variations and modifications thereof may be made without departing from the underlying principles and scope of the invention. 1 therefore desire, by the following claims, to include all such variations and modifications by which substantially the results of my invention may be obtained through the use of substantially the same or equivalent means.

I claim:

1. A hydraulic elevator comprising, in combination, an elevator pit, vertical guides extending upwardly from said pit, an elevator cab disposed immediately adjacent said guides for vertical translation therealong, a hollow metal cylinder extending vertically downward from said pit, a cab support plunger extending from said cab downwardly into said cylinder, an annular seal encircling said plunger between the lower end thereof and the upper end of said cylinder to form a sliding seal between said plunger and said cylinder, a metal outer head secured transversely to the lower end of said cylinder in closing relation thereto by an impervious peripheral weld, a metal safety head disposed transversely within the lower end of said cylinder a short distance above said outer head and secured to said cylinder by a circumferentially continuous weld extending around the entire periphery of said safety head, a pressure fluid operating conduit connected into said cylinder below said seal and above said safety head, said safety head defining a small safety orifice extending therethrough between the cylinder space above said safety head and the cylinder space between said heads, said safety orifice being dimensioned to respond to a dumping of fluid pressure from said space between said heads while operating fluid pressure is maintained in said cylinder above said safety head by releasing fluid through the orifice at a rate which causes said plunger and said cab to descend at a safe yet un mistakable speed, and a pressure responsive signal device connected to said cylinder space between said heads.

2. A hydraulic elevator having a predetermined rated load capacity and comprising, in combination, a long metal cylinder adapted to extend vertically downward into the earth, a long elevator support plunger depending longitudinally into said cylinder and extending thereabove, an elevator platform mounted on the upper end of said plunger for support and vertical movement thereby, an annular seal encircling said plunger between the lower end of the latter and the upper end of said cylinder to form a slidable seal between said plunger and cylinder, an outer head secured transversely to the lower end of said cylinder in closing relation thereto, a safety head disposed transversely within the lower end of said cylinder a short distance above said outer head and secured circumferentially to said cylinder, said safety head defining therein fluid passage space extending between the upper and lower sides of the safety head and having a size which is just suflicicnt to provide a rate of fluid flow therethrough which is approximately equal in cubic feet per minute to five times the transverse sectional area of said plunger in square feet when a differential fluid pressure is applied across said safety head equal to the fluid pressure within said cylinder incident to loading of said platform to the rated capacity of the elevator, and

an operating fluid conduit connected into said cylinder between said annular seal and said safety head,

3. A hydraulic elevator comprising, in combination, a hollow metal cylinder adapted to extend vertically down into the earth, an outer head secured to the lower end of said cylinder in closing relation thereto by an impervious weld extending around the entire periphery of the head, a safety head disposed within the lower end of said cylinder and extending thereacross a short distance above said outer head, means on said cylinder sup porting said safety head against downward movement, said safety head defining therein a small fluid flow space extending from the space above the safety head into the space between the two heads, a vertical plunger reciprocably disposed in said cylinder and extending vertically thereabove, an annular seal encircling said plunger between the lower end thereof and the upper end of said cylinder to form a slidable seal between said plunger and said cylinder, an operating fluid conduit connected into said cylinder between said seal and said safety head, a differential pressure responsive safety device connected to the space above said safety head and to the space between said heads to operate in response to significant differential fluid pressure across said safety head, and an elevator platform mounted on the upper end of said plunger.

4. A hydraulic elevator comprising, in combination, an earth embedded vertical cylinder, an extendable plunger depending into said cylinder and extending upwardly therefrom, an elevator platform mounted on the upper end of said plunger, an annular seal fixed to the upper end of said cylinder and closely encircling said plunger to form a slidable seal therewith, an outer head on the lower end of said cylinder closing the latter, a conduit for operating fluid connected into said cylinder below said seal, a safety head disposed transversely within said cylinder below the connection thereto of said conduit and spaced a short distance above said outer head, means on said cylinder providing a strong peripheral support to said safety head, and said safety head defining a circular safety orifice extending downwardly therethrough into the space between said heads and having a transverse diameter in English units equal to thirteen-thousandths of the transverse diameter of said plunger multiplied first by the fourth root of the quotient obtained by dividing the maximum operating pressure in the cylinder into the mass density of the operating fluid supplied through said conduit and multiplied further by the second root of a descent velocity of approximately five feet per minute.

5. A hydraulic elevator comprising, in combination, an earth embedded vertical cylinder, a plunger depend ing into said cylinder and extending upwardly therefrom, an elevator platform mounted on the upper end of said plunger, an annular seal encircling said plunger between the lower end thereof and the upper end of said cylinder to form a slidable seal between said plunger and cylinder, an outer head mounted on the lower end of said cylinder in closing relation thereto, a safety head mounted transversely within the lower end of said cylinder a short distance above said outer head to define a safety plenum chamber between the two heads, said safety head defining therein a safety orifice extending between said plenum chamber and the cylinder space above the safety head, said orifice being dimensioned to discharge fluid from above the safety head at a rate which effects lowering of said plunger and platform at a safe unmistakable rate of descent when the orifice is subjected to a differential pressure thereacross approximately equal to the fluid pressure required in said cylinder to sustain the plunger, and an operating fluid conduit connected into said cylinder between said annular seal and said safety head.

Furlow Apr. 26, 1910 Jansson Apr. 20, 1915 

